Typically the point and angle of entry of a surgical needle (such as a biopsy needle) in a patient is first calculated by scanning the patient via an imaging technique such as computed tomography (CT) or magnetic resonance imaging (MRI) with imaging surface markers placed on the patient (such as the torso). The point of needle entry is typically selected with reference the most appropriate imaged position marker and the angle of needle entry in relation to the plane of the scan calculated by the scanning machine computer. An operator's then has to estimate the calculated needle entry angle for example with assistance from a protractor at the end of the bed before inserting the surgical needle into the patient.
After the initial needle entry into the patient, trial and error is then usually required to reposition the surgical needle via reentry of the surgical needle and further scans to make contact with the target (such as a lesion, fluid collection or during radio or microwave tissue ablation). The disadvantage of this procedure is the protracted operation time with multiple needle entries which can lead to discomfort and increased radiation exposure to the patient with CT scanning.
Known apparatus for guiding a surgical needle include the SeeStar device disclosed in http://apriomed.com/products/seestar/. The disadvantage with these known devices is that they are still relatively imprecise in matching the exact angle of entry of the surgical needle in axial and cranio-caudal planes to that calculated by an imaging machine, in that the apparatus has to be configured with the predicted angle of entry before attaching to the body of a patient, which may result in a change in the actual angle of entry after attachment if the patients body surface is not flat. In this way, known devices still frequently require repeated needle entry and scans to achieve a successful biopsy.
More recently, robotic automated image guided stereotactic apparatus are known which are designed specifically for use in determining the position and angle of entry of a needle into a human patient (used primarily in brain surgery). However these apparatus are bulky, costly to maintain with expensive software upgrades and difficult to operate, requiring highly specialist surgical skills.
Consequently there is a need for a cost effective and less intrusive diagnostic apparatus whereby the angle of entry of a surgical needle can be configured on the apparatus after placement on the body of a patient.